Fire and temperature alarm.



as the simplest form enoncr.

LAWRENCESMITH, OF LON DON, ENGLAND.

FIRE AND TnivxrnnAT aE ALARM.

To all whom it may concern:

Be it known that I, Gnonen LAWRENCE SMITH, a subject of the King of Great Britain, residing in. London, England, have invented certain new and useful Improvements in Fire and Temperature Alarms, of which the following is a specification.

My invention relates to alarms of the socalled rate of rise type, in which the alarm is initiated through the expansion of air contained in a small-bore metal tube passing through the protected zone and communicating with pressure-responsive means for transmitting a signal upon the 00- currence of any sudden and unusual increase of pneumatic pressure Within the tube. Such an alarm is illustrated and described in my United States Letters Patent No. 850,681, granted April 16, 1907. Inthat patent I set forth that the tube, which communicates at one end with the detector, must be effectively closed at the other end,an

of such structure illustrated and described a tube in which the end reiiiote from the detector was actually sealed. I havediscovered that this efiective I as copper,

closure of the end of the tube remote from the detector is in some instances not necessarily an actual sealing of the tube, but may be accomplished in a variety of ways without departing from the beneficial mode of operation described in my prior Patent No.

850,681. a r I My present invention is directed to certain ot er means of efiecting the closure of the remote end of the tube, as will appear more fully below. I

In the accompanyi drawings, which form a part of this specification, Figure 1 is a diagrammatic view of a room equippe with my improved fire or temperature alarm system. Fig. 2 is a view showing the detector in elevation and a modified closure for the remote end of the tube. Fig. 3 is a side elevation ofthe detector shown in Fig. 2 in connection with a further modified form of closure for the far end of the tube.

Referring to the drawings in detail, the numeral 1 designates the detector tubing extending through the area to be protected or supervised by the alarm. This tubing is preferably constructed of metal having a.v

reasonably high thermal conductivity, such and may have an outside diameter of one-tenth of an inch with a bore of one-twentieth of an inch, although these di- Specificationof Letters Patent.

Application filed December 4,

' nection.

1915. Serial No. 64,978.

mensions may be increased or decreased both I Patented Dec. 11, 1917.=

as regards the diameter and the bore, to sult 1 special conditions. The tubing isarranged', 1n the protected zone in the manner. de; scribed in my prior Patent No. 850,681 and. terminates at one end in a detector 2, which need not be described in tector illustrated and described in my prior patent is satisfactory for use in this con- Instead of sealing the far end tubing, that is, the end'remote from the tector, I find that it is, factory to continue the tubing for a consid:

a of the detail, since the de in many cases, sat s erable distance beyond the point3 where it end in case it were herwould naturally The extreme end 4 ofjthe metically sealed.

tubing is then left open to the atmosphere. 4 I

Owing to the small bore of the tubing used, the added length, diametrically illustrated as extending 'from 3 to 4in Fig. 1, is such 1 that the skin or internal friction of the con-- fined air against the tube is sufii cient topre vent the sudden and unusualg increase in pressure generated in the tube 1 by a fire or abnorma condition within the protecte' 'zone, from being dissipated by leakage past the end 4: to an extent suflicient to prevent thetransmission of an alarm.

while this internal an efiective closure for the far end of the tube, so that the operationaof the system is in other respects identical with the mode of operation described inzm (prior atent, still there are certain add cial instancesarising from treme end 4 of the tube 0 ento the atmos phere. For example, in all systems of this general type, it is-necessary to: provide a leak, as described in my former patent, for permitting a compensation and balancing of the pressures between atmospheric pressure and that within the'tube, resulting =from normal changes in temperature and changes in barometric pressure. The; closure, WhlCl'l .is constituted by the extra length of tubin At the same time,-j or skin friction acts as;

the main portion of temperature nefitsin speleaving. the ex- I god , length which it of the tubing 3-4 is coiled up. This coiling of the tubing increases the internal or skin friction, and, therefore, the length of tubing which needs to be added to the normal installation to act as the efi'ective closure for the far end of the tube, is less than the length which is required in the case of straight runs of tubing 3-4, such as shown in Fig. 1.

In Fig. 3 I have shown a further modification in which to the. end 3 of the main stretch of tubing is added a short length of tubing 5 of decreased bore. Since the skin friction increases with decrease in diameter of the tubing, it will be obvious that the stitute the effective closure of the remote end of the tubing, is much smallerwhen tubing of a reduced diameter is employed.

It will thus be seen that in all three modificationswhich I have illustrated the principle of operation is identical With that of the apparatus illustrated, described and claimed in my prior patent, one end of the tubing in each case entering the detector and the remote end being efi'ectively closed. v While I have illustrated and described only certain embodiments of my invention I realize that it is capable of wide adaptation without departing from the spirit of the invention of my prior Patent N 0.

850,681, and I do not ,desire to be limited to the precise construction shown and described herein.

Having thus described my invention, I claim:

1. In a fire and temperature alarm in combination, a metal tube of small diameter having a correspondingly small bore conis necessary to add to con taining air, a closed chamber, the interior of which communicates with the bore of the tube, said tube having a predetermined effective area, means operated by a sudden and unusual increase of pneumatic pressure in the effective area of the tube and in the chamber, for initiating an alarm, and means for compensating for a slow rate of temperature rise, sald latter means consisting of an extension of said tube beyond its normally effective area.

2. In a fire and temperature alarm in combination, a metal tube of smalldiameter having a correspondingly small bore containing air, a closed chamber, the interior of which communicates with the bore of the tube, and means operated by a sudden and unusual increase of pneumatic pressure in the tube and chamber for initiating an alarm, a portion of'the tube remote from said chamber being of reduced bore and open to the atmosphere, but efl'ectively closed against the dissipation of any sudden and unusual increase of pneumatic pressure Within the intermediate portion of the tube.

3. In a fire and temperature alarm the combination, of a chamber, a small metal -tube having a correspondingly small bore communicating therewith and having a predetermined normally eifective area, means embodied within said chamber and adaptdd to be operated by the sudden expansion of air in said tube to initiate an alarm, said tube being extended beyond this normally efi'ective area to compensate for the gradual expansion of'the' air therein under the normal variations in the atmospheric temperature.

GEORGE LAWRENCE SMITH. 

